1. Field of the Invention
The present invention relates to an integrated circuit package.
2. Background Information
Integrated circuits are typically assembled into a package that is mounted to a printed circuit board. FIG. 1 shows an integrated circuit package commonly referred to as a plastic ball grid array (PBGA) package. The PBGA package includes an integrated circuit 1 that is mounted to a substrate 2. Bond wires 3 may connect the integrated circuit 1 to a top surface of the substrate 2. The integrated circuit 1 and bond wires 3 may be enclosed by an encapsulant 4.
The package has a plurality of solder balls 5 that are attached to a bottom surface of the substrate 2. The substrate 2 is typically a printed circuit board which has routing traces, vias, etc. which electrically connect the integrated circuit 1 to the external solder balls 5. The solder balls 5 are reflowed to attach the package to a printed circuit board 6.
The integrated circuit 1 generates heat which must be removed from the package. Some integrated circuit packages incorporate heat slugs, heat sinks and other thermal elements which are attached to the top surface of the package. The additional thermal elements can add to the complexity and cost of mass producing the package.
A portion of the heat generated by the integrated circuit 1 may flow into the printed circuit board 6 through the solder balls 5. The thermal impedance through the solder balls 5 is inversely proportional to the area of the balls 5. The solder balls 5 have a relatively small cross-sectional area. The relatively small solder ball area therefore creates a relatively high thermal impedance. The junction temperatures of the integrated circuit are proportional to the thermal impedance of the balls. A higher impedance increases the junction temperatures for a given amount of heat. It would be desirable to provide a PBGA package that more efficiently transfers heat into the printed circuit board than packages of the prior art.